Silicone elastomer line prosthetic devices and methods of manufacture

ABSTRACT

Organopolysiloxane elastomers comprising copolymers of dimethyl and methylvinyl siloxanes provide improved facial and dental prosthetic materials, and are especially useful in preventing and treating chronic tissue irritation due to hard dental polymers. They are effectively bonded to polymeric and metallic substrates as denture liners, obturators, maxillofacial prosthetic devices and appliances with a group of trifunctional silane coupling agents.

This is a division of copending application(s) Ser. No. 07/519,165 filedon May 4, 1990, now U.S. Pat. No. 5,112,640.

BACKGROUND OF THE INVENTION

This invention relates generally to prosthetic devices and methods ofmanufacture, and more specifically, to maxillofacial prosthetic devicesand dental appliances having permanent silicone elastomers bondedthereto forming composite structures with enhanced strength, dimensionalstability and elasticity.

Prosthodontic devices, such as dentures typically consist of a baseplateof a hard resin, such as poly(methyl methacrylate) which supports theartificial teeth for chewing, and also enhances esthetics. Difficultycan arise, however, due to the inability of patients to tolerate thehard baseplate. As a result, there is need for a resilient liner whichmay be affixed to the denture base to cushion soft tissues of the oralcavity. Ideally, such materials should be permanently resilient, inert,cleanable, substantially water insoluble, have low water-sorptionproperties and good tensile and tear strength. While softness isdesirable for comfort, the liner must also be sufficiently firm todisplace soft tissues of the mouth and permit grinding of the dentureperiphery to avoid creating sore spots. From a practical view point, thedental appliance should also be capable of fabrication under conditionsgenerally found in dental laboratories, avoiding extremes in temperatureand pressure, or the need for special equipment.

Laboratory and clinical studies have shown that few, if any, of thepresent materials used as resilient liners and prosthetic devices, forexample, are satisfactory in all respects. Most common shortcomingsinclude inadequate strength and elasticity, high rate of water diffusionthrough the elastomer and subsequent staining and deterioration.Frequently, with the discovery of a potentially improved prosthodonticmaterial having what might appear to be fewer of such shortcomings, thematerial is compromised due to the inability to satisfactorily bond theelastomer to dental base plastics and other prosthetic appliances.

Accordingly, there is a need for improved facial and dental prostheticelastomeric materials possessing properties of strength, elasticity,dimensional stability, low water sorption and toxicity, includingmethods which enable convenient bonding to most dental base polymerswith a high degree of permanence and reliability. Such materials andmethods would be useful in fabricating prosthodontic devices, such asdentures with improved elastomeric liners for preventing and treatingchronic tissue irritation from hard dental polymers and for cushioningsoft tissues; liners after oral surgery, maxillofacial prostheticdevices, like obturators for defects in the palate, and the like.

SUMMARY OF THE INVENTION

Accordingly, it is a principal object of the invention to provide amethod of forming a composite-like structure of a silicone elastomer,generally referred to as an organopolysiloxane, and a prostheticappliance by the steps of:

a) applying a film of a coupling agent to the appliance, the couplingagent comprising a compound of the formula:

    X--Si--(R).sub.3                                           (I)

wherein X is methyl or vinyl and R is --O--CO--CH₃ or--O--N═C--(CH₃)--CH₂ CH₃ ;

b) drying the silane film on the appliance;

c) applying to the dried silane film on said appliance a siliconeelastomer to form the composite-like structure, the elastomer comprisinga copolymer of dimethyl and methylvinyl siloxanes, the elastomer when inthe form of about a 0.075 inch thick slab, press cured for about 10minutes at about 230 to about 250° F. and cured for about 24 hours atabout 21° to about 25° C. and at a relative humidity of about 45 toabout 55 percent is characterized by a specific gravity ranging fromabout 1.08 to about 1.12 as determined by ASTM D 792; a Shore Adurometer in a range from about 19 to about 27 as determined by ASTM D2240; a tensile strength of at least 1100 psi as determined by ASTM D412, Die C; an elongation of at least 1050 percent as determined by ASTMD 412, Die C; a tear strength of at least 140 ppi as determined by ASTMD 624, Die B, and

d) curing the composite structure at above ambient temperatureconditions.

Prosthetic appliance as mentioned herein is intended to mean principallyprosthodontic devices, such as dentures, obturators, splints, etc.However, the present invention also contemplates polymeric and steelbased, e.g. stainless steel, prosthetic devices for other portions ofthe anatomy requiring a highly durable, nontoxic resilient materialtherefor. Thus, the expressions composite/composite-like as used hereinis intended to include such representative example as dentures havingresilient liners of the silicone elastomer firmly bonded to the base forprotecting oral tissues.

It is yet a further object of the present invention to provide for amaxillofacial prosthetic device, e.g. obturator, comprising a resilient,dimensionally stable silicone elastomer comprising a copolymer ofdimethyl and methylvinyl siloxanes. The elastomer when in the form ofabout a 0.075 inch slab, press cured for about 10 minutes at about 230°to about 250° F. and cured for about 24 hours at about 21° to about 25°C. and at a relative humidity of about 45 to about 55 percent ischaracterized by a specific gravity ranging from about 1.08 to about1.12 as determined by ASTM D 792; a Shore A durometer in the range fromabout 19 to about 27 as determined by ASTM D 2240; a tensile strength ofat least 1100 psi as determined by ASTM D 412, Die C; an elongation ofat least 1050 percent as determined by ASTM D 412, Die C, and a tearstrength of at least 140 ppi as determined by ASTM D 624, Die B.

A still further object includes oral post surgical devices having bondedthereto resilient, tear resistant, low water sorption, dimensionallystable silicone elastomers comprising the dimethyl and methylvinylsiloxanes. The elastomer when in the form of about a 0.075 inch thickslab, press cured for about 10 minutes at about 230° to about 250° F.and cured for about 24 hours at about 21° to about 25° C. and at arelative humidity of about 45 to about 55 percent is characterized by aspecific gravity ranging from about 1.08 to about 1.12 as determined byASTM D 792; a Shore A durbmeter in the range from about 19 to about 27as determined by ASTM D 2240; a tensile strength of at least 1100 psi asdetermined by ASTM D 412, Die C; an elongation of at least 1050 percentas determined by ASTM D 412, Die C; a tear strength of a least 140 ppias determined by ASTM 624, Die B.

DETAILED DESCRIPTION OF THE INVENTION

The composite structures of the invention are based on the discoverythat a particular grade of organopolysiloxane elastomer, described ingreater detail below, possesses unique properties making it adaptable toa wide range of medical and dental prosthetic applications, withparticular emphasis on the fields of prosthodontics and maxillofacialprosthetics, including liners for dentures, interim prosthesis,transitional prosthesis, splints, speech aid devices and obturators. Asmaxillofacial materials the organopolysiloxane elastomers may be used tocorrect facial defects resulting from surgery, accidents, or evencongenital deformities. Noses, ears and eye orbits, or other parts ofthe head and neck may be replaced by protheses fabricated from thesematerials, allowing patients to lead a more normal life. It should beunderstood, however, that the invention is not limited to dental andfacial applications, but also contemplates prosthetic applications forother parts of the body whenever the need exists for a resilient, butdimensionally stable, inert medical grade elastomeric material.

The organopolysiloxane elastomers have been found to be especiallyuseful in conjunction with prosthodontic appliances, such as permanentsoft lining materials used to replace the fitting surface of a hardplastic denture, either because the patient cannot tolerate a hardfitting surface, or to improve retention of the denture. Otherrepresentative applications include maxillofacial devices, such asobturators typically fabricated from a dental base resin and a resilientlining which locks above the margin of the cleft, thus providingretention of the appliance. Other representative composite applicationsmay include Duyzings' plates fabricated from a hard acrylic resin andsoft lining inserts.

The organopolysiloxane elastomer coatings and liners are characterizedby high elongation, softness, but with dimensional stability andenhanced resistance to tearing, along with low water absorption. Theelastomers and their method of preparation are described in detail inU.S. Pat. No. 3,445,420 which is incorporated-by-reference herein. Thegenerally preferred organopolysiloxanes are those copolymers of dimethyland methylvinyl siloxanes having from about 99.90 to about 99.99 molepercent dimethyl siloxane units and from about 0.01 to about 0.10 molepercent methylvinyl siloxane units. They are also commercially availablethrough ordinary channels of commerce from Dow Corning, Midland, Mich.,under the registered trademark, SILASTIC, and includes such grades ofsilicone elastomers having the manufacturer's designation Q7-4720. Theyare supplied by the manufacturer as a two-component kit having separatepouches designated parts A and B. The contents of each can be blendedtogether manually to form the desired elastomer without requiringspecial equipment, such as a roll mill. Pouches A and B contain theSiloxane copolymer and the reinforcing filler, fumed silica. Theplatinum based curing catalysts for increasing molecular weight, whichare added to part A only without the elastomer curing, are alsodisclosed in U.S. Pat. No. 3,445,420. Part B also includes anorganoacetylenic curing inhibitor, preferably an acetylenic alcohol,together with a crosslinking agent.

The most preferred SILASTIC brand elastomer is that designated Q7-4720which is a copolymer comprising dimethyl and methylvinyl siloxanes inwhich approximately 99.95 to about 99.97 mole percent is dimethylsiloxane and approximately 0.03 to about 0.05 mole percent ismethylvinyl siloxane. When parts A and B are blended together and formedinto a slab of about 0.075 inch thickness, press cured for about 10minutes at about 230° to about 250° F. and cured for about 24 hours atabout 21° to about 25° C. and at a relative humidity of approximately 45to about 55 percent SILASTIC Q7-4720 can be characterized by a specificgravity ranging from about 1.08 to about 1.12 as determined by ASTM D792; a Shore A Durometer of about 19 to about 27 as determined by ASTM D2240; a tensile strength of at least 1100 psi as determined by ASTM D412, Die C; an elongation of at least 1050 percent as determined by ASTMD 412, Die C, and a tear strength of at least 140 ppi as determined byASTM D 624, Die B.

While manufacturer's literature on the above elastomers refers to themas --medical grade ETR (enhanced tear resistant) elastomers--, suchliterature provides no specific teaching or suggestion the elastomerscan be used in forming composite-like structures, such as permanentlining materials for prosthodontic appliances, e.g. dentures, withoutdelaminating or separating from the denture base. SILASTIC brandsilicone elastomer grade Q7-4720, according to manufacturer'sliterature, is suggested in fabricating devices for the health careindustry where high elongation and softness are important, such as inballoons, encapsulating and in extrusions. In addition, such literatureoffers no solution to the problem of how to form strong, reliable bondsin fabricating composite structures with hard plastics, like theacrylics, for example. U.S. Pat. No. 3,445,420 suggests theorganopolysiloxanes as coating compositions for metal, wood and glass,but also fails to suggest, or provide other enablement how theelastomers can be laminated to hard polymer substrates to providestrong, reliable bonds therewith.

Accordingly, this invention not only relates to the discovery of a newuse in the field of prosthetics for a specific group oforganopolysiloxane elastomers, but also contemplates novel methods forreliably bonding them to hard substrates, e.g. prosthetic devices toform composite-like structures, without which the elastomers could notbe readily employed. This aspect of the invention is especiallysignificant since prior methods and materials successfully employed inbonding silicone elastomers to a substrate have not been found to be areliable basis for predicting bonding performance with other elastomers.That is, coupling agents and know-how successfully employed in bondingother grades of dental/medical elastomers to form composite structureshave not proven useful in forming satisfactory laminated structures withthe silicone elastomers disclosed herein.

Hence, the present invention also contemplates the discovery of aparticular group of silane coupling agents and protocols for bonding theforegoing organopolysiloxane elastomers to prosthetic devices. Thesilane coupling agents found useful in forming permanent bonds with theparticular silicone elastomers of the invention to prosthetic devicesfall within Formula (I) above. Specific representative examples ofespecially useful silane coupling agents are methyltriacetoxysilane,vinyltriacetoxysilane, methyltris(methylethylketoximine)silane andvinyltris(methylethylketoximine)silane. The foregoing silanes are knowncompounds, and are commercially available through ordinary channels ofcommerce from Petrarch Systems, Bristol, Penna., under cataloguedesignations M8980, V4800, M9220 and V5050, respectively.

The initial step of forming the composite structure provides forapplying the liquid coupling agent to the surface of the dentalappliance or other medical device as is, or as a more economic dilutesolution, e.g. 25 percent by volume in a suitable solvent, such asmethyl methacrylate monomer. For bonds of optimum strength, more than asingle coat is preferred. In addition, each coating is preferably driedbefore applying the next coat, and so on. Most preferably, the silanepainted substrate is oven dried above ambient temperature conditionsafter the final coating of coupling agent has been applied.

Suitable substrates for the composite-like structures comprise materialscommonly used in fabricating prosthodontic appliances, such as acrylics,polyesters, polyurethanes and other resinous materials, as well ascertain metals, like stainless steel, aluminum, cobalt and chrome. Someof the most widely used hard materials in dentistry are the denture baseresins which can also be used in forming the composites. They includethe acrylics, such as poly(methyl methacrylate) (PMMA), rubber modifiedacrylics, vinyl acrylic copolymers, hydrophilic acrylics, fluidacrylics, and so on. Other useful denture base materials are theglycol-modified poly(ethylene terephthalates) which are available underthe trademark KODAR PETG copolyester 6763, a clear amorphous polymeravailable from Eastman Chemical Products, Inc., Kingsport, Tenn.; andurethane polymers, such as a visible light curable urethanedimethacrylate polymers available under the trademark TRIAD fromDentsply International, Inc., York, Penna.

Frequently, dental polymers like PMMA contain polymerization initiators,such as ABIN or benzoyl peroxide. The presence of such initiators in thepolymeric material may contaminate the platinum catalyst system of thesilicone elastomer, and consequently, the elastomer may not fully cure.For this reason it is preferred that the hard polymeric substrates ofthe composite structure be in a precured condition, substantially freeof such initiators.

The resilient silicone elastomer previously described can then beprepared and applied to the silane coated denture base or otherprosthetic device to provide an appropriate liner, protective coating,etc. Because SILASTIC grade Q7-4720 will cure at room temperature aswell as at elevated temperatures, Parts A and B of the two part materialare manually blended at this stage and applied to the dried silanecoated surface employing techniques which assure intimate contactbetween the uncured elastcmer and silane coated substrate. Such methodsare generally known by persons of ordinary skill. The coated/linedprosthetic appliance is then cured at elevated temperatures to form thecomposite, generally in the range of approximately 60° to 90° C., andmore preferably, at about 70° to about 80° C. This may be performed byplacing the mold assembly holding the composite in a compressed state ina water bath or in a circulating convection oven where curing takesplace over a period of hours.

The following specific examples demonstrate the methods and articles ofthe invention. However, it is to be understood that these examples arefor illustrative purposes only and do not purport to be whollydefinitive as to conditions and scope.

EXAMPLE I

In order to perform comparative studies and also demonstrate the bondstrength of composite structures according to the invention, testdenture base materials consisting of rigid acrylic resin (PMMA)rectangularly shaped having a dimension of 7.5 cm×2.5 cm×4 mm thicknesswere prepared. Prior to application of the coupling/bonding agent, theacrylic specimens were lightly abraded with a sandblaster or 240 gritabrasive paper, rinsed and stored in room temperature water. Beforeapplication of the coupling agent, the acrylic specimens were dried andcleaned with methanol. A 25 percent solution of a vinyltriacetoxysilanecoupling agent in methylmethacrylate monomer was brushed onto onesurface of each rectangular shaped rigid denture base specimen as a thincoating and allowed to air dry at room temperature for 5 minutes. Asecond coating of the coupling agent was applied over the first coatingand dried for 30 minutes in an oven at 70° C.

Equal parts by weight of packages A and B of Dow-Corning's SILASTICQ7-4720 Medical grade ETR silicone elastomer were thoroughly blendedtogether manually on a plate. Individual silane coated acrylic sectionswere seated in gypsum molds with a separating medium previously appliedand the blended elastomer packed against each section. Two or threetrial packings were used with excess flash removed between each step.The mold assembly was then cured at 74° C. for 8 hours in a water bath.The test strips thus consisted of 4 mm thick rigid acrylic backing witha 3 mm thick lining layer bonded over 5 cm of specimen length. Bondedtest pieces were stored at 37° C. for 30 days prior to testing.

Ends of the peel test specimens were secured in serrated grips with thesoft lining tab bent back to give a peeling angle of 180°. The unit wasplaced on an INSTRON testing apparatus.

This machine uses interchangeable resistance strain gage cells whichmeasure tensile or compressive loads. Load is applied with a constantstrain rate by motion of the crosshead which carries the moving jaw.Stress-strain recordings are made on a chart which moves insynchronization with the crosshead.

Test specimens were subjected to a peeling force by separation of thegrips at a crosshead speed of 30 cm/min. Force per unit width of thebond necessary to cause detachment of the elastomers was calculated asdetermined by ASTM D 903 and presented in Table I.

EXAMPLE II

In order to demonstrate the performance ofvinyltris(methylethylketoximine)silane (V-5050) andvinyltriacetoxysilane (V-4800) as coupling agents for the siliconeelastomer SILASTIC Q7-4720, specimen samples were prepared according tothe protocol outlined in Example I. Samples were prepared using bothundiluted coupling agent and dilution with methyl methacrylate monomerto provide 25% solutions. Control specimens were fabricated withoutsilane coupling agent.

For comparison, peel strength determinations were also performed on acommercial soft liner material, MOLLOPLAST B, available through BuffaloDental Supply Co., New York, N.Y. MOLLOPLAST B is a peroxide catalyzed,heat-cured silicone rubber. Analysis of the MOLLOPLAST B coupling agent,PRIMO, seems to show it is a vinyltriethoxy silane in methylmethacrylatemonomer. Peel strength specimens were prepared as follows.

Test denture base materials consisting of rigid acrylic resin (PMMA)rectangularly shaped having a dimension of 7.5 cm×2.5 cm×4 mm thicknesswere prepared. Prior to application of the coupling/bonding agent, theacrylic specimens were lightly abraded with a sandblaster or 240 gritabrasive paper, rinsed and stored in room temperature water. Beforeapplication of the coupling agent, the acrylic specimens were dried andcleaned with methanol. The liquid bonding agent, PRIMO, was brushed ontoone surface of each rectangular shaped rigid denture base specimen as athin coating and allowed to air dry at room temperature for 90 minutes.

Individual coated acrylic sections were seated in gypsum molds and theone part MOLLOPLAST B silicone packed against each section. Three trialpackings were used with excess flash removed between each step. The moldassembly was then cured at 74° C. for 8 hours in a water bath. The teststrips thus consisted of 4 mm thick rigid acrylic backing with a 3 mmthick lining layer bonded over 5 cm of specimen length. Bonded testpieces were stored at 37° C. for 30 days prior to testing.

Ends of the peel test specimens were secured in serrated grips with thesoft lining tab bent back to give a peeling angle of 180°. The unit wasplaced on an INSTRON testing apparatus. Test specimens were subjected toa peeling force by separation of the grips at a crosshead speed of 30cm/min. The force per unit width of the bond necessary to causedetachment of the elastomer was calculated and presented in Table I.

                  TABLE I                                                         ______________________________________                                        BOND STRENGTH kN/m                                                            MATERIAL               MEAN     SD                                            ______________________________________                                        Q7-4720 (100% V5050)   10.50    .82                                           Q7-4720 (25% V5050)    9.04     1.22                                          Q7-4720 (100% V4800)   10.59    1.91                                          Q7-4720 (25% V4800)    10.88    1.22                                          Q7-4720 (CONTROL-NO SILANE)                                                                          1.65     .30                                           MOLLOPLAST-B           .15      .07                                           ______________________________________                                         N = 10 PER MATERIAL                                                      

Bond strength testing indicates the tenacity of the bond between theelastomer-acrylic composite. This test provides an indication of theclinical success of a resilient liner.

The data (Table I) shows that the bond strength of SILASTIC Q7-4720 testspecimens with coatings of silane coupling agent is approximately tentimes greater than those Q7-4720 specimens with no silane (control).Also, Q7-4720/silane coated specimens failed with a thin layer of theelastomer attached to the acrylic substrate (cohesive failure) ratherthan by peeling of the bond between the elastomer and acrylic in thecontrol specimens (adhesive failure). In comparison with Q7-4720 testspecimens coated with 100% silane, those coated with a 25% solution ofsilane in methylmethacrylate monomer showed substantially nodeterioration in bond strength.

MOLLOPLAST B test specimens demonstrated a bond that exceeded thestrength of the material, i.e. the elastomer portion of the specimenruptured before a consistent peel was observed at relatively low forcelevels.

EXAMPLE III

An impression of the patient's existing upper or lower edentulous jaw istaken with the denture to be relined using conventional techniques. Theunit is invested in a dental flask forming a stone model. Such methodsare generally known by persons of ordinary skill. After the gypsum stonehas hardened sufficiently, the flask is gently separated. Immersion inhot (50° C.-60° C.) water for approximately 5 minutes may facilitateseparation. The impression material is removed and the denture base isprepared to provide sufficient space for the resilient liner, optimally2 to 3 mm in all areas. A tin foil substitute separating medium isapplied to all gypsum surfaces.

The acrylic surface which will contact the resilient liner is cleanedwith methanol. A 25% solution of vinyltriacetoxysilane coupling agent inmethylmethacrylate monomer is brushed onto the cleaned acrylic surfaceas a thin coat and allowed to dry 5 minutes at room temperature. Asecond coat is applied and dried 30 minutes in an oven at 65° C.-70° C.A blended mix of equal parts by weight of SILASTIC Q7-4720, A and B, isformed into a roll and placed onto the coated acrylic denture base.Trial packing twice with a thin plastic separating sheet will produce aneven distribution of material. The plastic sheet is removed prior toclosing the flask for processing. The mold assembly holding thecoated/lined prosthetic appliance in a compressed state is then placedin a water bath or circulating convection oven for 8 hours at 74° C. Theassembly is then cooled and the appliance removed from the flask. Thecured/bonded resilient liner is then trimmed and finished by standardtechniques.

EXAMPLE IV

Obturators may be used to seal defects in the head and face caused bycongenital clefts or surgical procedures. Although surgical repair maybe the treatment of choice, treatment with a prosthesis is oftenindicated. Former methods necessitated mechanical retention of theresilient obturator portion onto the rigid acrylic.

The construction of an obturator to seal a defect in the hard palate ofthe upper jaw is described. The obturator bulb portion may be hollow orsolid. The jaw may be edentulous, partially edentulous or having a fullcomplement of teeth. An impression of the upper jaw is taken usingstandard techniques. A positive stone model is made from the impression.After the gypsum stone has hardened sufficiently, the impression isgently separated. Immersion in hot (50° C.-60° C.) water forapproximately 5 minutes may facilitate the separation. The model is theninvested in a conventional dental flask. Such methods are generallyknown by persons of ordinary skill. The defect is blocked out with waxor other suitable medium and a plate processed in acrylic PMMA resinwith or without prosthetic teeth using standard techniques. The curedPMMA section is then separated from the stone model and the blockoutmedium is removed from the defect.

The margins of the obturator may line the entire palatal surface andterminate at the periphery of the acrylic. Alternatively, the obturatormargins may terminate at any portion within the outer border of theacrylic. The acrylic surface which will contact the lining/obturator iscleaned with methanol. A 25% solution of vinyltriacetoxysilane couplingagent in methylmethacrylate monomer is brushed onto the cleaned acrylicsurface as a thin coat and allowed to dry 5 minutes at room temperature.A second coat is applied and dried 30 minutes in an oven at 65° C.-70°C.

A blended mix of equal parts by weight of SILASTIC Q7-4720, A and B, isformed and placed into the defect and extended to the desired palatalcoverage. Severe undercuts within the defect may be blocked out with waxor other suitable medium. Trial packing twice with a plastic sheetbetween the rigid acrylic and SILASTIC Q7-4720 will produce an evendistribution of material. The plastic sheet is removed prior to closingthe flask for processing. The mold assembly holding the prostheticappliance in a compressed state is then placed in a water bath orcirculating convection oven for 8 hours at 74° C. The assembly is thencooled and the appliance removed from the flask. The cured/bondedresilient obturator/liner is then trimmed and finished using standardtechniques.

While the invention has been described in conjunction with specificexamples thereof, this is illustrative only. Accordingly, manyalternatives, modifications and variations will be apparent to personsskilled in the art in light of the foregoing description, and it istherefore intended to embrace all such alternatives, modifications andvariations as to fall within the spirit and broad scope of the appendedclaims.

What is claimed is:
 1. A prosthetic appliance comprising a denturehaving bonded thereto a resilient, tear resistant, low water sorption,dimensionally stable silicone elastomer liner consisting essentially ofa platinum-catalyzed organopolysiloxane copolymer of from about 99.90 to99.99 mole percent dimethyl siloxane units and from about 0.01 to about0.10 mole percent methylvinyl siloxane units, wherein the siliconeelastomer is bonded to the appliance with a coupling agent of theformula: X--Si--(R)₃, wherein X is selected from the group consisting ofmethyl and vinyl; and R is selected from the group consisting of--O--CO--CH₃ and --O--N═C--(CH₃)--CH₂ CH₃.
 2. A prosthetic appliancecomprising an obturator having bonded thereto a resilient, tearresistant, low water sorption, dimensionally stable silicone elastomercoating consisting essentially of a platinum-catalyzedorganopolysiloxane copolymer of from about 99.90 to 99.99 mole percentdimethyl siloxane units and from about 0.01 to about 0.10 mole percentmethylvinyl siloxane units, wherein the silicone elastomer is bonded tothe appliance with a coupling agent of the formula: X--Si--(R)₃, whereinX is selected form the group consisting of methyl and vinyl; and R isselected from the group consisting of --O--CO--CH₃ and--O--N═C--(CH₃)--CH₂ CH₃.
 3. A prosthetic appliance selected from thegroup consisting of a prosthodontic appliance, maxillofacial prostheticdevice, and an oral post surgical device, having bonded thereto aresilient, tear resistant, low water sorption, dimensionally stablesilicone elastomer liner consisting essentially of a platinum-catalyzedorganopolysiloxane copolymer of from about 99.90 to 99.99 mole percentdimethyl siloxane units and from about 0.01 to about 0.10 mole percentmethylvinyl siloxane units, wherein the silicone elastomer is bonded tothe appliance with a coupling agent of the formula: X--Si--(R)₃, whereinX is selected from the group consisting of methyl and vinyl; and R isselected from the group consisting of --O--CO--CH₃ and--O--N═C--(CH₃)--CH₂ CH₃.
 4. A prosthetic appliance selected from thegroup consisting of a denture, interim prosthesis, transitionalprosthesis, a splint, speech aid device, and an obturator, having bondedthereto a resilient, tear resistant, low water sorption, dimensionallystable silicone elastomer liner consisting essentially of aplatinum-catalyzed organopolysiloxane copolymer of from about 99.90 to99.99 mole percent dimethyl siloxane units and from about 0.01 to about0.10 mole percent methylvinyl siloxane units, wherein the siliconeelastomer is bonded to the appliance with a coupling agent of theformula: X--Si--(R)₃, wherein X is selected from the group consisting ofmethyl and vinyl; and R is selected from the group consisting of--O--CO--CH₃ and --O--N═C--(CH₃)--CH₂ CH₃.